1. Field of the Invention
The present invention relates to a rare probability connection call registration method using an incomplete call causation message for an asynchronous transfer mode (ATM) switching system, particularly for an ATM switching system which is capable of classifying the causes of the incomplete call by using the cause field within the release message in which the call release cause is registered in detail, and setting the call as an RPCC only when the resource of the relay switching system is lacking, or when the subscriber is on the line, to thus more accurately control the network, whereby it is possible to maximize the efficiency of the network resource by restricting the ineffective call.
2. Description of the Conventional Art
Most traffic congestion in a communication network occurs due to an overload in a receiving system. This communication congestion or overload of the switching system occurs due to the natural disasters, when too many call services are requested at one time, or when communication traffic is concentrated on a specific receiving system thus forming an unexpected communication failure.
When many calls are concentrated at a predetermined time at a specific receiving system (for example, reservations for public performance, or the audience response rating in a very hot television program is broadcasted), the above-described heavy call concentration phenomenon may occur even though an operator of the switching system predicts such heavy call congestion if some special operation preparations are not made on the system.
When call requests are heavily concentrated on a predetermined receiving number, that is when a large number of calls concentrated on the destination, beyond the design specification of the connection Admission Control function, the system can only offer limited service, and the system may go down due to the above-described problems.
FIG. 2 is a graph illustrating a performance variation when a switching system is overloaded.
As shown therein, the curved line "a" indicates a theoretical system performance which is obtainable when an overload of the system occurs or call traffic congestion occurs, and the curved line "c" denotes a system performance when the congestion control function is not operated, and the curved line "b" denotes the affordable system performance when the congestion control function is operated.
If the above-described situation is continuously maintained, the system congestion from many call attempts concentrated on a specific number may cause further congestion in a neighboring system, thus possibly culminating in a system-wide failure.
In order to overcome the above-described problems, a conventional public switched telephone network (PSTN) is directed to check a traffic completion ratio with respect to a candidate code (traffic received in a specific code of a predetermined system) that the operation input, and when a call completion ratio of a corresponding code is less than a predetermined threshold value, the call with respect to the corresponding code is controlled.
Such method is directed to maximizing the efficiency of the network so that system resources may be evenly distributed by detecting a receiving code in which the call completion ratio is lower than that of a normal call, and controlling the receiving code in a transmitter in which a desired call attempt is possible or the switching system near a transmitting terminal. Here, a call for which the completion ratio is lower is called a rare probability of a connection call (RPCC).
For conventional PSTN, the causes of incomplete calls are as follows. First, when the relay lines to a corresponding number from a first transmitter are all used, or when the switching resource of the transmitter (such as a call mixer, and a tone generator from resources of the communication) are scarce, the incompletion may occur. Second, a call is sometimes not connected due to the lack of switching resources of the relay system including the receiving system, and thus the incompletion may occur. Third, when a subscriber is on the line with another subscriber, or when the subscriber does not respond to the call, the incompletion may occur. Fourth, when the call is timed-out by the transmitting side of the subscriber, or when the subscriber ends the call, the incompletion may occur.
The transmitter processes the call attempt as an incomplete call by informing the transmitting side or the switching system of a ring back tone in the above-described state. However, when judging all of the call tone or the non-response of the subscriber to be in the RPCC, there may occur numerous system errors because RPCC means that the call completion ratio is lower with respect to a specific receiving signal. Therefore, it is necessary to measure the statistic value by the incomplete call due to the cause made by the destination side of the subscriber by classifying the call services by a failure cause.
In addition, when performing a function based on the candidate code, since the control is performed after a predetermined time after the operator inputs a predetermined code, it is impossible to prevent the call connection problems due to an unpredictable and sudden failure of the system in conventional method.